Lithographic wiping pad



W- 1963 P. A. MlTCHELL 3,396,420

LITHOGRAPHIC WIPING PAD Filed Jan. 27, 1966 United States Patent 3,396,420 LITHOGRAPHIC WIPING PAD Philip A. Mitchell, East Walpole, Mass., assignor to The Kendall Company, Boston, Mass., a corporation of Massachusetts Filed Jan. 27, 1966, Ser. No. 523,441 5 Claims. (Cl. -210) .ABSTRACT OF THE DISCLOSURE A multicomponent wiping pad suitable for lithographic work is produced by superimposing upon a fluid-spreading sheet of material a fluid-impervious barrier layer, an absorbent layer, and a relatively dense layer of absorbent fibers capable of exerting a mopping or cleaning function. Preferably the two surface layers are sealed to each other around their edges to form a unitary pad, which may have hingedly-connected portions of the bottom layer capable of being folded back on the body of the pad to form a handle. The result is a two-sided Wiping pad, one face serving to distribute fluid evenly over a lithographic plate surface, the other face serving to remove excess fluid.

This invention relates to a multicomponent, multipurpose wiping pad particularly adapted for the application, spreading, and removal of various liquids used in the graphic arts trade, particularly in lithographic reproduction.

In modern lithography, reproductions are made from specially-prepared metal plates, the preparation of which involves numerous wet processing steps such as cleaning, etching, coating with lacquer, retouching, inking, and the like. Involved in these processing steps are the application and subsequent distribution or removal of various aqueous and organic solvent solutions, such steps being carried out in various sequences depending on the particular nature of the reproduction to be made. Conventionally, the distribution of the various liquids, and the removal of excess, is effected by the use of fabric rags, paper, wads of fiber, or nonwoven fabrics. Natural and cellulose sponges are used to some extent, but contamination of the sponge is common and the relatively high cost necessitates reuse.

The use of conventional wiping materials in the preparation of lithographic plates has two disadvantages. First is the danger that the conventional wiping material will shed lint, which is picked up by the plate surface, interfering with the development of a proper image. A second drawback in conventional Wiping materials is that they are called on to perform two functions which are conflicting. First, they are used to spread a fluid evenly and uniformly over a metal plate, and with a uniformity which persists from plate to plate. Second, they are used to remove excess fluid from the plate, to leave a film which in final form may be less than one ten-thousandth of an inch in thickness. A wiping material which has sufficient absorbent capacity and high capillarity to serve efliciently in the wiping-off process will absorb into itself an excessive amount of fluid and give a poor distribution of fluid in the spreading process. Conversely, materials which will spread a thin fluid film over a metal printing plate are generally incapable of sequestering excess fluid.

It is an object of this invention to produce a two-sided Wiping pad for the preparation of lithographic plates, one face of said pad serving to distribute fluid evenly over the plate surface, and the other face serving to remove excess fluid.

The invention will be more clearly understood with reference to the following description and drawings, in which:

3,396,420 Patented Aug. 13, 1968 FIGURE 1 is a schematic cross-sectional view of a product of this invention.

FIGURE 2 is a view from above of a preferred embodiment of this invention.

FIGURE 3 is a perspective view, partly broken away, of the product of FIGURE 2.

FIGURE 4 is a view of the pad of FIGURE 3 with the tabs folded back, ready for use.

FIGURE 5 illustrates an alternative method of employing the pad of this invention.

Referring to FIGURE 1, a dual-purpose lithographic wiping pad 10 is shown as including a first surface layer comprising a relatively thin and fine-grained fibrous layer 12, in contact with a fluid-impervious barrier layer 14, upon which are superimposed a comparatively thick fluid absorbent fibrous layer 16 and a second surface layer in the form of another fibrous layer 18 in contact with the absorbent layer 16 and not separated therefrom by a barrier layer.

Layers 12 and 14 are preferably a unitary combination, and in the preferred form of my invention comprise a thermoplastic, fluid-impervious film 14 bonded to a light weight layer 12 of relatively fine-denier fibers (1.5 to 3 denier). The fibers may be in the form of a non-woven fabric, or the fibers may be unbonded inter se except by embedment in the thermoplastic film in accordance with the process set forth in US. patent application Ser. No. 514,079, filed Dec. 15, 1965. Alternately, a fine-grained thin fabric layer 12 may be bonded or adhesively laminated to the film layer 14, or a nonwoven fabric may be coated with a fluid-impervious coating to comprise the combination of layers 12 and 14. It has been found important that in order for the fibrous layer 12 to provide a proper distribution of lithographic fluid by a sort of squeegee action, the combination of fiber layer 12 and barrier layer 14 should have a combined retentive capacity, in a standard test in which it is immersed in liquid for 2 minutes and drained for 2 minutes, of not over 100%, and preferably between 25% and of its own weight in fluid. That is, although the lowermost layer 12 is fibrous, it shall be so selected and so combined with the barrier layer 14 that it holds only a thin layer of the fluid to be applied, and distributes it evenly over the plate. The use of film alone as the bottom layer of this composite Wiping pad is not satisfactory, since it is incapable of retaining and distributing fluid evenly.

As the barrier layer 14 I prefer, for convenience in processing, a thermoplastic film. Polyethylene, polypropylene, plasticized cellulose acetate, polyvinyl chloride, and the like are quite suitable. Alternately, the thin fibrous layer 12 may be adhesively united to a film which is of itself not thermoplastic, but is provided with a thermoplastic or adhesive coating. It is important, for the proper function of this portion of the pad, that the barrier layer 14 shall be impermeable and inert to the fluids, both water-based and organic-solvent based, used in the processing of lithographic plates. For this reason, polypropylene is preferred because of its flexibility and its resistance to ketonic and alcoholic fluids upon which lithographic lacquers are based.

The absorbent layer 16 performs no absorbing function in the wiping-on or fluid spreading phases of preparing lithographic plates, since the fibrous layer 12, usedto spread fluid, cannot transmit the fluid through the barrier layer 14. The layer 16 does absorb fluid from the top absorbent layer 18 when the latter is used to pick up and sequester all excess fluid from the plate sunface, as explained more fully below. The layer 16, during the fluid spreading phase, does serve to cushion and reinforce the spreading action, and provides desirable bulk to allow the operator to manipulate the pad easily. Preferably it should constitute at least 75% of the weight and thickness of the pad, and may comprise cellulose wadding, blown wood pulp, layers of soft absorbent tissue paper, and the like. Since this layer is protected on both surfaces, it need not have any significant wet strength. Cellulose wadding is an especially preferred material for the layer 16, since because of its crimped surface and its alternating areas of high and low fiber density it has rapid capillary spread and adequate absorbent capacity, serving to prevent excess fluid from accumulating in the wipe-oflf layer 18.

Layer 18, used to pick up and sequester traces of fluid in order to provide a dry, clean plate, is an absorbent layer characterized by high capillarity and comparatively high density. Conveniently it comprises fibers so arrayed as to have an apparent density of between 0.3 and 0.6 gram per cubic centimeter, and preferably in the range of 0.4 to 0.5 gram, compared with the density of cellulose as about 1.5 gnams per cubic centimeter. Soft, feltlike nonwoven fabrics, such as are widely used for fluid application, will retain within themselves pools or ca-lized puddles of fluid when used to pick up excess fluid. Such materials generally have an apparent density of 0.1 to 0.2, and their use for fluid sequestration leads to smearing and improper plate preparation. The layer 18 should not act as a fluid reservoir, but should through its high capillarity transmit most of the excess fluid to the reservoir layer 16. The range of preferred fiber density as expressed above has been found as ideal for this purpose.

Nonwoven fabrics are my preferred material for the absorbent layer 18. They may be bonded by polymeric binders, or may comprise binder fibers united to cellulosic fibers by heat and pressure. Alternatively, the fibers of layer 18 may be needled to a film or fabric base, or otherwise aggregated, provided that an apparent fiber density of between 0.3 and 0.6 is attained.

In order to maintain the layers of the pad in position during use, they may be adhesively united at the edges by conventional methods. A preferred embodiment, however, and one which provides an extra degree of convenience in use, is shown in FIGURES 2 and 3.

Referring to FIGURE 2, advantage is taken of the fact that the upper layer 18, or the barrier layer 14 of FIGURE 1, or both, may be of a thermoplastic and heatsealable nature. The lower layers 12 and 14 are shown in FIGURE 2 as being in the shape of an eight-sided figure formed of a central rectangular section, opposing sides of which are provided with wing-like tabs 20. In FIGURE 3, the upper layer 18 and the lower layers 12 and 14 of the preferred embodiment have been heatsealed along the four edges of the main body of the pad, as at 22, by means of heat and pressure applied to said edges, causing the thermoplastic film barrier layer 14 to melt and bond or weld together locally the thin fibrous bottom layer 12 and the top nonwoven layer 18, as shown at 15; This leaves the inner absorbent layer 16 unbonded but encapsulated in a sealed envelope.

In this manner a unitary pad is formed, in which the working faces are represented by the central rectangular area. The tab areas 20, composed of the bottom fibrous layers 12 and 14, extend beyond the rectangular central area to form a pair of tabs or wings which can be folded back across either the top or the bottom of the pad, thus forming a convenient purchase for the operator to grasp the pad, in either the spreading or the pick-up stages of plate preparation, without his fingers being stained by the solutions being applied. Since many operators are or become sensitized to the reaction fluids used in lithographic work, the advantages of this embodiment of the invention are obvious.

An alternative and preferred method of utilizing the pad of this invention, particularly useful in applications where considerable force must be applied to the plate, is shown in FIGURE 5. The tabs 20 of the pad, composed of the combined layers 12 and 14 as shown in FIGURES 3 and 4, are in FIGURE 5 folded back against an inverted T-shaped block of appropriate dimensions to fit the size of the sealed-edge pad. This T-shaped block consists of a horizontally-disposed rectangular member 32 and a vertically-disposed rectangular member 30 integral therewith. The block may be of any suitable rigid or semirigid material such as metal, wood, plastic, or heavy cardboard. FIGURE 5 shows the pad ready for the wiping-on or spreading operation. After such an operation is completed, the block is removed, the pad is turned upside down, and the wings 20 are refolded against the vertical element of the block, thus presenting the wipe ofl surface 18 to the plate.

Having thus described my invention, I claim:

1. A multicomponent, multipurpose wiping pad which comprises:

a fluid-spreading first surface layer comprising textile a fluid-impervious barrier layer in immediate face-toface contact with said first surface layer,

a bulky absorbent layer in face-to-face contact with and superimposed upon said barrier layer, and a second surface layer in face-to-face contact with and superimposed upon said bulky absorbent layer,

said second surface layer comprising absorbent fibers aggregated to an apparent density of between 0.3 and 0.6 gram per cubic centimeter,

said first surface layer and said barrier layer being provided at a pair of opposing edges with a pair of hingedly-connected segments capable of being folded back over the main body of the pad to provide a handle,

said second surface layer being coextensive with only a part of said first surface layer and said barrier layer and being bonded thereto on at least two of its edges,

the component layers constituting said wiping pad being fixed in position against lateral displacement relative to each other when the pad is used.

2. The product according to claim 1 in which both surface layers are nonwoven fabrics.

3. The product according to claim 1 in which the barrier layer is a polyolefinic film.

4. The product according to claim 1 in which said fluid-spreading first surface layer and said fluid-impervious barrier layer are adhesively united substantially throughout their coextensive contact areas.

5. The product according to claim 4 in which the second surface layer is adhesively united around all of its coextensive contact edges with said first surface layer and said barrier layer.

References Cited UNITED STATES PATENTS 3,315,676 4/1967 Cooper 161-151 X 2,029,951 2/ 1936 Smith.

3,124,822 3/1964 Marchese 15-118 3,142,855 8/1964 Gilchrist 15-210 3,149,364 9/1964 Baptist et a1. 15-506 3,280,420 10/1966 Wanzenberg 15-506 3,284,963 11/1966 Lanham et a1 15-209 X CHARLES A. WILLMUTH, Primary Examiner. L. G. MACI-ILLN, Assistant Examiner. 

